New Block Triangular Preconditioners for Saddle Point Linear Systems with Highly Singular (1,1) Blocks

Table 6

Number and time of iterations of GMRES(10) with preconditioners ℳ_𝐭 for different drop tolerances 𝜏 and 𝐭 when ℎ=1/24.

𝜏	𝑡=1/2	Time (1/2)	𝑡=2	Time (2)	𝑡=4	Time (4)	𝑡=8	Time (8)
0.01	9(87)	3.36	3(22)	0.87	3(27)	1.03	4(34)	1.30
0.005	8(79)	3.02	2(19)	0.88	3(23)	0.90	3(28)	1.14
0.001	6(52)	2.17	2(16)	0.78	2(19)	0.78	3(22)	1.00
0.0001	4(38)	1.77	2(14)	0.75	2(15)	0.73	2(16)	0.83